System for producing an aperiodic vibrato signal

ABSTRACT

A system for producing a vibrato signal which varies in frequency in a manner uncorrelated with time in an electronic musical instrument, in which at least two dissonant signals are applied to a control input of each tone generator via a gate circuit, a divider chain and a low-pass filter.

Emailed Sfiates Paient Van Der Peel, deceased et al. 1 May 22, 1973 [54]SYSTEM FOR PRODUCING AN [56] References Cited APERIODIC VIBRATO SIGNALUNITED STATES PATENTS [75] Inventors: Cornelis Johannes Van Der Peel,

deceased; by Casper Antonius Help 13; sent; ..84L./2152)5( urvl l g j3,440,325 4/1969 Schwartz et a1. ..84/1.25 l dh N th 1 ds 3,701,04010/1972 Borl'evik et 2.1.... .....84/1.25 X masmge 6 an 2,322,884 6/1943Roetker ..s4 1.25 x 73 Assignee; Philips c ti New 3,157,725 11/1964Wayne ..84/ 1.24 York, 3,479,440 11/1969 Martm et al ..84/1.25

[22] Filed: Sept 20, 1971 Primary Examiner-Richard B. Wilkinson [21]Appl. N0.: 182,068 Assistant ExaminerSt an1 ey J. WitkowskiAttorneyFrank R. Tnfan [30] Foreign Application Priority Data [57]ABSTRACT Sept. 22, 1970 Netherlands ..70l3955 A System for producing avibrato signal which varies in frequency in a manner uncorrelated withtime in an [52] US. Cl ..84/1.25, 331/178 electronic musical instrumentin which at least two [51] hit. Cl. ..G10h 1/02 dissonant signals areapplied to a control input of each [58] Fleld of Search ..84/l.24, 1.25,DIG, 4, tone generator via a gate circuit a divider chain and a 84/D1G.10, DIG. 11, 1.01, 1.03; 331/106, low pass filten 4 Claims, 2 DrawingFigures SYSTEM FOR PRODUCING AN APERIODIC VIBRATO SIGNAL The inventionrelates to a system for producing a vibrato signal which varies infrequency in a manner uncorrelated with time, in an electronic musicalinstrument provided with at least one tone generator.

Such a system is described in U.S. Pat. No. 3,267,199, in which theoutput signal of an organ is shifted in frequency to the ultrasonicrange and then is returned to the initial frequency range by means ofthe same auxiliary oscillator. Before the signal of this auxiliaryoscillator is returned, it is passed through a filter which varies thephase as a function of a second signal. The latter signal may be a noisesignal or a lowfrequency signal, as is usual for a vibrato. It will beappreciated that such a system is comparatively complicated and hencecomparatively expensive.

According to the invention, at least one gate circuit is provided havinginputs which are connected, as the case may be, through a pulse shaper,to at least two sources of signals which preferably form a discordwithin an octave, a control input of each tone generator being coupledto an input of one of the gate circuits via at least one divider-by-twochain.

Thus, there will appear at the output of the last divid er-by-two chainor divider-by-two chains, a signal which consists of pulses ofcontinuously varying width, which are spaced by intervals which differfrom one another in a manner such that the mean pulse duration is onehalf of the mean period. The combination of the signals applied to thegate circuit is chosen so that the mean period of the signal at theoutput of the last divid er-by-two chain or at the outputs of the lastdivider-bytwo chains correspond to the period of the signals usuallyemployed for the vibrato.

If, in an embodiment of a system according to the invention, each lastdivider-by-two chain is followed by a low-pass filter having a cut-offfrequency of a value between one and four times the reciprocal of themean period of the signal at the output of the last divider-bytwo chain,there will appear at the output of this filter, a low-frequency signalwhich has the nature of band noise. Applying this signal to a controlinput of a generator, the frequency of this generator can be variedstatistically about its mean value, so that the sound from thisgenerator will assume the nature of a wind instrument, such as a flute,an organ-pipe, etc.

In a further embodiment of a system according to the invention, each ofthe signals applied to a gate circuit consists of one of the tonesignals produced in the instrument.

It will be clear that such a system is simple, because the signals usedare produced in the instrument in any case, so that no additionaloscillators are required.

A particularly advantageous embodiment of a system according to theinvention includes a gate circuit which is connected to the controlinputs of all the tone generators via each divider-by-two chain and viathe lowpass filter, if provided.

The term control input of a tone generator is used in this specificationto mean an input to which the application of a signal of varyingmagnitude results in a frequency variation of the tone generator. Thisincludes, for example, that part of the supply circuit of which theoutput voltage feeds the generators. The output voltage may be varied bymeans of the signal from the gate circuit, so that the frequencies ofthe generators vary.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying diagrammatic drawings, in which FIG.1 is a circuit diagram of a system according to the invention using fourgate circuits, and

FIG. 2 is a circuit diagram of a system using one gate circuit.

Referring now to FIG. 1, l2 tone generators G G are each connected to adivider-by-two chain D D in each of which chains the frequency of thetone of the associated generator is divided by a factor of 2, so that atthe outputs of these divider chains, the lower octave tones areavailable. The system includes four gate circuits P R, which each havethree inputs which each are connected to an output of one of the dividerchains D D if required, i.e. if the signals at the output of the dividerare not sufficiently pulseshaped, through a pulse shaper I, I,respectively. In this case out of the divider chains D D four groups areformed each consisting of three divider Chains b 2 3; 4, 5 6; 1 8, 9; 1011 12) whereby the tones at the respective outputs of these dividerchains form dissonant intervals of a minor second, so that the gatecircuit P is connected to the divider chains D D and D the gate circuitP is connected to the divider chains D D and D etc.

The outputs of the gate circuits P P are each connected to a seconddivider chain B B, which each comprise at least one divider-by-twostage, with the result that at the output of each of these dividerchains B B, a pulsatory voltage appears, the mean period of which,corresponds to the period of a signal usually employed for producing avibrato. The output of each of the divider chains B B is connected to alow-pass filter F F respectively, having a cut-off frequency which isbetween one and four times the reciprocal of the mean period of thesignal at the output of the respective divider chain B B Without theprovision of this low-pass filter, the pulsatory signal would cause thegenerator frequency at the output of the respective divider chain B B tobe aperiodically and abruptly shifted, from the minimum frequency to themaximum frequency, whereas now the integrating nature of the low-passfilter F F causes the frequency to vary more gradually.

The signal at the output of each filter F F is, respectively applied tothe control input of one of the four sets of three generators G G and GG G and G respectively, so that the frequency of these generators variesin a manner uncorrelated with time.

The outputs of the low-pass filters F F need not necessarily beconnected each to the associated set of generators G,, G and G G G and Gbut may alternatively be connected to any other set of three generators.As a further alternative, a different number of gate circuits may beused which each have at least two inputs, provided that each generatoris connected to an output of a filter.

FIG. 2 shows a particularly advantageous circuit arrangement in whichonly one gate circuit P is used which has 12 inputs which each areconnected to one of the outputs of one of the 12 divider chains D D Theoutput of the gate circuit P here also is connected to a divider chain Bthe output of which is connected to a low-pass filter F. The output ofthe low-pass filter F is connected to the control inputs of all twelvegenerators G G This circuit arrangement provides highly satisfactoryresults if the frequencies of the signals applied to the gate circuitslie between 1,000 Hz and 2,000 Hz, and if the divider stages B 3., againdivide these frequencies by a factor of, for example, 16.

The cut-off frequency of each of the low-pass filters F E, has beenchosen to be about 15 Hz.

Obviously in instruments provided with a single generator which is tunedto a different frequency by each key, as will be the case in melodyinstruments, or from the signal of which all the other signals withinthe octave are derived, the output of the low-pass filter F must beconnected to the control input of this one generator only.

The number of signals applied to the gate circuit, the frequency rangefrom which these signals are taken, and the number of divider-by-twochains at the output of each gate circuit, together determine the meanperiod, the pitch range, and the repetition rate of the vibrato signal.

What is claimed is:

l. A system for producing a vibrato signal which varies in frequency ina manner uncorrelated with time in an electronic musical instrument,comprising:

a gate circuit;

a plurality of pulse shapers connected to said gate circuit at inputsthereof;

a divider stage connected to said gate circuit at an output thereof;

a plurality of tone generators each having a control input;

a low pass filter connected between the divider stage and each controlinput of said tone generators; and divider chains connected between saidtone generators and said pulse shapers.

2. The system of claim 1, wherein said low pass filter is connected to aset of three generators.

3. The system of claim 1, wherein the low pass filter has a cut-offfrequency lying between approximately one and four times a reciprocal ofa mean period of a signal appearing at an output of the divider stage.

4. The system of claim 1, wherein at least two dissonant signals areapplied to said control input of each tone generator.

1. A system for producing a vibrato signal which varies in frequency ina manner uncorrelated with time in an electronic musical instrument,comprising: a gate circuit; a plurality of pulse shapers connected tosaid gate circuit at inputs thereof; a divider stage connected to saidgate circuit at an output thereof; a plurality of tone generators eachhaving a control input; a low pass filter connected between the dividerstage and each control input of said tone generators; and divider chainsconnected between said tone generators and said pulse shapers.
 2. Thesystem of claim 1, wherein said low pass filter is connected to a set ofthree generators.
 3. The system of claim 1, wherein the low pass filterhas a cut-off frequency lying between approximately one and four times areciprocal of a mean period of a signal appearing at an output of thedivider stage.
 4. The system of claim 1, wherein at least two dissonantsignals are applied to said control input of each tone generator.